The sampling covariance matrix, VSFull, associated with this expanded SFull covariance matrix includes a number of components. One block of this VSFull matrix, VSLDSC, contains the sampling variances and sampling covariances of the latent genetic variances (SNP heritabilities) and genetic covariances, which are obtained from the multivariable LDSC approach introduced above. A second block of the VSFull matrix, VSSNP, is composed of the sampling covariance matrix of the SNP effects on the phenotypes. The SNP variance (derived from reference panel data) is treated as fixed, and its sampling variance and sampling covariance with all other terms are fixed to 0 (or to a very small value to facilitate computational tractability). The sampling covariances of the SNP-genotype covariances with one another are obtained using cross-trait LDSC intercepts (which represent sampling correlations weighted by sample overlap) after being rescaled relative to the sampling variances of the respective SNP-genotype covariances.11,44 A final block of the VSFull matrix represents the sampling covariance of the SNP-genotype covariances with the genetic variances and genetic covariances. These are fixed to 0, as sampling variation of the SNP-genotype
